Sickle cell retinopathy.

Sickle cell hemoglobinopathies are caused by the presence of one or more abnormal hemoglobins, causing red blood cells to acquire abnormal shapes under conditions of hypoxia and acidosis. The deformed red blood cells are more rigid than healthy cells and may clump together and cause obstruction of small-caliber vessels, with subsequent tissue ischemia and severe local acidosis and hypoxia, and even greater sickling of the cells. Sickle cell anemias with mutations in hemoglobins S and C are inherited as alleles of normal hemoglobin A and cause significant visual complications.

Abnormal hemoglobin can be combined with normal hemoglobin A in different variations.

1. AS (sickle cell type) occurs in 8% of people with dark skin color. This is the mildest form and is usually accompanied by acute hypoxia.
2. SS (sickle cell anemia) occurs in 0.4% of people with dark skin color. It causes acute systemic complications with pain syndrome, crises, infarction, and acute hemolytic anemia. Ocular manifestations are minor and asymptomatic.
3. SC (sickle cell anemia) occurs in 0.2% of people with dark skin color.
4. SThal (sickle cell thalassemia): Both SC and SThal are associated with mild anemia with acute ocular manifestations.

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Proliferative sickle cell retinopathy

Most acute forms of retinopathy are more often associated with the SC and SThal forms and less often with the SS form.

Clinical features of sickle cell retinopathy

Stages of Sickle Cell Retinopathy

• Stage 1. Peripheral arteriolar occlusion.
• Stage 2: Peripheral arteriovenous anastomoses arising from pre-existing dilated capillaries. The retinal periphery beyond the area of vascular occlusion is avascular and nonperfused.
• Stage 3. Proliferation of new vessels from anastomoses. Initially, newly formed vessels do not rise above the retinal surface, have a blurred configuration, are fed by a single arteriole and drained by a single vein. From 40 to 50% of such areas undergo spontaneous involution as a result of autoinfarctions with the appearance of grayish fibrovascular changes. In other cases, the proliferation of neovascular bundles continues, they contact the cortical vitreous body and can bleed as a result of the formation of vitreoretinal tractions.
• Stage 4: Vitreous hemorrhage following relatively minor eye trauma.
• Stage 5. Significant fibrovascular proliferation and tractional retinal detachment. Rhegmatogenous retinal detachment is possible if a tear forms near an area of fibrovascular tissue.

Foveal angiography reveals extensive areas of nonperfused capillaries in the periphery of the retina (see Fig. 14.926) and late leakage from newly formed vessels.

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Treatment of sickle cell retinopathy

Peripheral retinal photocoagulation is performed in the area of non-capillary perfusion, which causes regression of neovascular tissue in patients with recurrent vitreous hemorrhages. However, unlike diabetic retinopathy, new vessels in sickle cell anemia tend to autoinfarct and spontaneously involute without any treatment.

Pars plana vitrectomy is of little benefit in the treatment of tractional retinal detachment and/or recurrent vitreous hemorrhages.

Non-proliferative sickle cell retinopathy

Asymptomatic disorders

• Tortuosity of the veins due to the presence of peripheral arteriovenous shunts is one of the first eye symptoms.
• The "silver wire" symptom of arterioles in the periphery is represented by previously occluded arterioles.
• Irregularly shaped pink spots, preretinal or superficial intraretinal hemorrhages at the equator, near arterioles, resolve without a trace.
• "Black radiance" is represented by zones of peripheral hyperplasia of the retinal pigment epithelium.
• The symptom of macular depression is represented by the suppression of the bright central macular reflex and is caused by atrophy and thinning of the sensory retina.
• Peripheral "hole-shaped" retinal breaks and areas of "white without pressure" type blanching are observed less frequently.

Symptomatic disturbances

1. Occlusion of the paromacular arterioles occurs in approximately 30% of cases.
2. Acute central retinal artery occlusion is rare.
3. Occlusion of retinal veins due to increased viscosity is not typical.
4. Choroidal vascular occlusion is rare and occurs mainly in children.
5. Angioid streaks of the retina appear in isolated cases.

Extraretinal changes

Changes in the conjunctiva are characterized by isolated dark red corkscrew-shaped changes in small-caliber vessels, which are most often localized in the lower sections.

Changes in the iris are represented by limited areas of atrophy due to ischemia, most often at the pupillary margin, spreading to the ciliary belt. Rubeosis is rarely observed.